feat(sim+player): scale-ring navigation (endless encoder) + cosmos/abyss scales

Add scale-ring navigation to the simulator per the scales-library design §3:
an endless rotary-encoder control (relative, vs the absolute 0-4 experience
knobs) walks a closed ring of neutral "scales of nature" clips, with placeholder
AI zoom/warp transitions between adjacent scales and a small->large wrap (the
infinite-zoom payoff).

- player/ring.py (new, canonical pure logic): ScaleRing + advance_ring; one
  transition clip per edge, played forward zooming inward / reversed outward;
  modulo wrap both ways; chained steps for a multi-detent spin. Mirrors
  player/content.py conventions (frozen dataclasses, pure functions).
- simulator: load_ring + ring_to_dict/ring_move_to_dict; GET /api/ring and
  POST /api/ring/advance (Python owns step/wrap/transition math; the browser
  only plays the returned transition(s) then settles on the target scale).
- frontend: endless-encoder control (zoom in/out buttons + stage scroll),
  current-scale readout, multi-clip active-scale selection, transition playback.
- media: two cheap true-PD scales so the ring is demonstrable -- cosmos
  (NASA/Hubble) + abyss (NOAA Ocean Exploration), provenance recorded in the
  manifest, bytes generated as labelled placeholders by setup_scales_media.py.
  The expensive multi-strength flow-stabilized Right re-bake is DEFERRED (new
  scales carry a raw base only) until the ring is liked; Pi renderer +
  serial/firmware remain deferred (simulator-first).
- docs: ROADMAP slice-3 done; USER_GUIDE scale-ring gesture; plan doc.

Verified: pytest 215 passed / 2 skipped (+22 new); sim boots, /api/ring +
/api/ring/advance correct incl. wrap, media served, and a headless-Chrome CDP
drive walked cosmos -> forest -> abyss -> (wrap) -> cosmos with the active clip
reloading correctly.

Spec: docs/superpowers/specs/2026-06-07-scales-library-and-right-axis-pipeline-design.md (§3)
Plan: docs/superpowers/plans/2026-06-07-scale-ring-navigation.md

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/USER_GUIDE.md

@@ -298,12 +298,16 @@ piece moved from *selecting* clips to *altering* them.)
 **One-time setup — populate the sample footage** (look-tuning only; not shipped
 content):
 
-    python simulator/setup_sample_media.py
+    python simulator/setup_sample_media.py    # the forest scale (real POC base + Right variants)
+    python simulator/setup_scales_media.py    # the cosmos + abyss scales + ring transitions
 
-This copies the session-0008 POC artifacts (`~/hef-poc/out/`) into
-`simulator/sample_media/forest/` — the neutral base clip and the real
+`setup_sample_media.py` copies the session-0008 POC artifacts (`~/hef-poc/out/`)
+into `simulator/sample_media/forest/` — the neutral base clip and the real
 flow-stabilized Right restyle — and generates placeholder intermediate Right
-strengths. The `.mp4` binaries are gitignored.
+strengths. `setup_scales_media.py` makes the scale **ring** demonstrable: cheap
+synthetic placeholder bases for the two true-PD scales (`cosmos` = NASA/Hubble,
+`abyss` = NOAA Ocean Exploration) plus the per-edge zoom/warp transition clips.
+The `.mp4` binaries are gitignored.
 
 **Run it (Docker):**
 
@@ -320,6 +324,13 @@ then open http://localhost:8000.
 
 - **Content dial** — picks audio/video channel; "off" and audio-only positions go
   to black walls.
+- **Scale ring (endless encoder)** — `⊖ out` / `in ⊕` (or scroll the stage) walk a
+  *closed ring* of neutral "scales of nature" clips — cosmos → forest → abyss and
+  back around (diving past the smallest **wraps** to the largest). It is *relative*
+  (an endless encoder), distinct from the absolute 0–4 knobs: each step plays a
+  short placeholder zoom/warp **transition**, then settles on the next scale, with
+  the current knob alteration still applied. The current scale is named beside the
+  buttons (`name (i/N)`).
 - **Four experience knobs (0–4):**
   - **Dark / Light** — a live runtime color grade (cool/dark ↔ warm/bright; equal
     or zero = the raw footage).